well your radio has lost its ability to stay locked on to a station, obviously. this could happen most likely by a bad capacitor (as stated above). but it is possible that a bad potentiometer or coil comming out of alignment can cause the radio to tune incorrectly, but since u say its tuning in correctly, then wondering off, there are some screwed up tank circuits or something in there. so definatley a hardware problem. its old, time for new technology!